1. Field of the Invention
The invention relates to a safety device for an underground liquefied gas storage cavity or chamber.
2. Description of the Prior Art
FIG. 1 of the appended drawings is a diagrammatic vertical sectional view taken through a conventional storage cavity. The type of gas, the various conditions, the depth levels and dimensions may be different within certain limits. This Example is given only to introduce the problems which are encountered by the operating staff. Further, so as to limit the figure size, without reducing too much the interesting parts thereof it is better not to abide by the proportions.
Generally, the storage shown in FIG. 1 includes a well 1 and a series of galleries or chambers 2 which can be of any form and disposition, such as comb teeth, parallel galleries or chambers and pillars and the like.
Well 1 is covered by a concrete slab 5, at the ground level 93, or at least above the underground water level. The isolation of the storage from the atmosphere is made in the junction well, above the galleries, or near the ground, by a concrete closure 11. The well extends under the floors of the galleries so as to form a water sunk draining trap 12. The well portion which is above closure 11 may be full of water (level 9). The draining trap receives the underground seeping water, and can receive it up to a predetermined level 14. In some other cases, the well may be fitted with a watertight lining or tubing, the upper end of which is closed by a metal cap, welded and pressure resistant. All the tubes of intercommunication run through this cap. The galleries shown in FIG. 1 are used to receive the stored product, especially hydrocarbons. A liquid phase 16 of the product can reach the level indicated at 15 and the gaseous phase 4 fills the higher part of the storage, particularly the upper part of the well, under isolation cover 11.
A plurality of tubes 17, 18, 19 extend from the outside to several levels in the storage, and are connected outside to various implements schematically designated at 20. At the bottom, the seeping water flows permanently through the galleries, runs over the gallery floor and is collected in the draining trap from where it is extracted by an immersed pump (FIG. 3) so as to be held at a suitable level, as it will be discussed thereafter.
Pipe 17 is used for the extraction of the stored product and pipe 18 for the seeping water. The water pump is servo-controlled in such a manner that the water level or water-hydrocarbon interface 14 is kept between the suction openings of pipes 17 and 18. If the water level rises up above tube 17 opening, it is no longer possible to pump hydrocarbon. Should the level lower too much, the water pump would discharge hydrocarbon. Tubes 17 and 18 are each formed by a fixed sheath and contain a discharge pipe which supports a motor and pump unit with the electric or hydraulic control devices used for the operation of motors, pumps, valves or other fittings or accessories.